John R. Copeland ) wrote:

Mike, add special emphasis to the reading of the Z-scale numbers.
The NOAA radar depiction sets their lowest color level (cyan)
at -24 to -28 dBZ when no storms are shown on the presentation,
but when storms are present, the same color is +5 to +10 dBZ.
That's why a casual look at the radar can mislead the unwary
to mistake wet clouds for a rainstorm. The dBZ numbers rule.

I got burned by the sensitivity of the Nexrad display last March. I was
flying down to Wings Field (north of Philly, PA) from central NY when
radar depicted what looked like a line of t-storms approaching mid-PA.

After seeing this on the ADDs weather site, I was going to cancel but
instead decided to call Flight Service for a briefing. It was then that
I learned the red radar returns were from snow, not heavy liquid precip.
The briefer had told me that most likely the radar was more sensitive
than it would have been during the summer, which made the returns look
much stronger than they were.

Had I seen the key, I would have determined this myself.

--
Peter